Tension control device



Oct. 19, 1954 TENSION CONTROL DEVICE Filed April 29, 1950 3 Sheets-Sheetl w 7 yfiw' J. B. KOHLER 2,692,091

Oct. 19, 1954 J. B. KOHLER 2,692,091

TENSION CONTROL DEVICE Filed April 29, 1950 3 Sheets-Sheet 2 Marzeeys.

Oct. 19, 1954 J. B. KOl-ILER TENSION CONTROL DEVICE 5 Sheets-Sheet 3Filed April 29, 1950 Z rzz/enzor "'d'mTE,

7&7??? ,3. fiakZer @EVA Patented Oct. 19, 1954 UNITED STATES ATENTOFFICE This invention relates toa method andan' apparatus forcontrollingthe tensionwinding and unwinding devicesor. assemblies; It'hasfor. oneobject to provide automatic means for. maintaining constant the tensionon-.a-web, forsexampl'e, of paper, whichis being unwound.

Another object is toprovide. automatic. compensation for misadjustmentof a tension: controlling' device; and also to provide automaticcompensation as a result of operating conditions Figure 3' is a partialtop-view ofa portion of the mechanism of Figure 1, takenfrom ab'ove onan enlarged scale with parts omitted and' parts in'section; and

Figure 4 is a schematic diagram illustrating the electrical and i thefluid f pressure circuits embodied in the mechanism.

Like partsare indicated" by like characters throughout the specificationand the drawings.

Asshown, theinvention is applied to anunwindingmechanism. The particularform shown is suitable for use with machines-to'which paper or other webmaterial is fed for treatment or for printing. Such a mechanism mayconveniently'be-used in connection'with a-web-fed printing press.unwinding'device where the paper is-to be treated. As shown,- themechanism comprises standards lthat may conveniently be fixed on' afoundation' 2'. A- shaft 3 is supported in bearings 4 which arethemselves carried by the standards I.

Fixed on the shaft 3 aretwo arm members '5, one preferably adjacent eachend of the shaft 3': The arms 5 carry bearings 6- adapted removably toreceive mandrelsl upon which rolls of paper or otherweb Band 8 mayconveniently a bewound.

Means not here shown in detail are provided for moving the shaft 3 andthe arms and the rolls which are rotatably mounted on the arm sothat therolls are successively brought into a 1 It may also be used with' almostany i 13 Claims. (Cl. 242-75) the. position of use. Such an. assembly isknown as a magazine reel,iand isgenerally' available commercially;

Such a magazine reel: may be equipped with devices for controlling thetension of the: unwindingrolls, which will'be hereinafter described, andalso with. devices permitting changingzfrom an expiring roll. to' a.fresh .roll' at. speed, known generally as Flying Paster' devices which.are also. generally known and available commercially and, therefore. notdescribed herein.

The particular form'of tension device disclosed herein, includes a:system of" belts 9:with' attendant pulleys, shafts and otherdevices;later described, including: a drivenlshaft lli with keyedpulleys l 0 engaging said 'belts 9; a means of draw.- ing orpullingonthe web,- normally a part of" the printing press or other machine to:which the web is supplied, anda mechanical orotherrpositivedrive'connecting the two..

The belts'e passfrom thepulleys l0=to pulleys I4 keyed on a shaft l5.Thence, the beltspass partially about the-upper roll 8 from whichunwinding is taking place, and about idlerpulleys I6 and to idlerpulleys ll and about compensating pulleys Ill. The compensating pulleysl8 are mounted on short shaftsl9; each of which is carried in a cage 20.Each cage 2'0"isconnected to a piston rod 2t, and each piston rod:is=connected to a piston 22, then mounted for reciprocation in acylinder 23; The cylinders 23* and the cages 20 are mounted onguide rodswhich are carried at their'upper'ends on a rod or'support 25 upon whichthe idler' pulleys H are mounted.

At their lower ends the guide rods are secured on a rod or support 26.The cylindersare fixed on the guide rods, and the cages are mounted forreciprocation thereon. The pulleys l0; IB and l1 and theshafts whichcarry them may be supported from the frame 21 which may form part of abuilding or be otherwise provided; so long as it is sufficiently strongand rigid to support the parts mentioned.-

Frame or supporting members 28- are carried from the standards I asshown in Figures 1 and 2. The rod 26 and the shaft l5 are supported inthese frame members.

Mounted also in the frame or support members 28 is an idler roller 29carried on-a shaft 3i]. Another idler roller 3! is carried on an armwhich is counterweighted as at 33 and supported on suitable bearings,-as at'34:

The pulleys l4 and'the shaft l5 upon which they are keyed have'beenmentioned above. As

or other fluid under pressure.

in connection with the description of the operation of the entiredevice.

A housing or protecting member 39, fixed on a support 40, may bepositioned about the brake assembly. The member as is secured to theadjacent frame member 28. If desired, a central or intermediate support4| may be provided for the shaft l5. If such a support is present, anantifriction bearing 42 will be carried by the sup- .port and willfurnish a support for the shaft intermediate its ends. End bearings 43are also provided for the shaft l5, and these end bearings are carriedin the frame or support members 28.

As the web 44 of paper or other material is unwound from the uppermostor active roll 8, it passes about the roller 31 and thence about aroller 45, about the roller 29 and about the rollers 46 and 4'! in theprinting press or other machine to which the web is being supplied.

The roller 45 is carried in arms 48 which are fixed on a shaft 49 in theframes or supports 28. Counterweights 59 are carried on opposite ends ofthe arms 48. One or more springs 50' are secured to one or both of thearms 48 as shown in Figure 1. They tend to pull downwardly on the arms48 so as to pull or move the roller 45 downwardly. An adjusting means 85is provided for adjusting the tension of the springs 54.

Fixed on the shaft 49 are two switch-operating arms. They comprise thearms 51 and 52. Associated with the arm is a switch 53, and associatedwith the arm 52 is a switch 54. The

operation and function of the switches will be described below. v

Bumper or limit members 55 are provided for the counterweights 5i! andare mounted on a tube or rod 56 which is itself connected to the frames28.

In Figure 4 the pressure fluid circuit which operates the brake, and thepiston and cylinder assemblies are shown. The pressure fluid mayconveniently be air and is supplied through a main conduit 51 from anysuitable source of air The fluid for operating the brake passes througha conduit 58, through a reducing and relief valve 59, and thence to athree-way control valve 40. A gauge 6| may be positioned in the line 58,if desired. The movable member of the three-way valve 60 is operated byan arm 62 which, through a link 63, is connected to the armature E4 of asolenoid 65. As shown in Figure 4, the valve 60' is in the normal orinactive position, and pressure fluid may bleed out through the conduit38 and the discharge 66.

When pressure fluid is to be applied to the brake, the solenoid isactuated by the switch 54, and the movable element of the valve 56 isturned to cause the passage of fluid under pressure from the conduit 58to the conduit 38, and finally to the brake operating means.

The main conduit 57 passes through a reducing and relief valve 61 andthence through a manually operable valve 68, thence to a bleeder valve69, and finally to conduits in. This valve as is arranged when thesolenoid is energized to open the conduit to the atmosphere through arestricted opening for the purpose of reducing the pressure within theconduit while the valve is open. One such conduit is provided for eachof the cylinders 23. A gauge H may be provided if desired. In each ofthe conduits iii a manually operable shut-off and adjusting valve 12 isprovided.

The valve 69 is operated by means of a lever 13, which through a link 14is connected to the armature 15 of a solenoid 16. The operation of thissolenoid is controlled by the switch 53 through the movement of the arm5!. Suitable electrical connectors are provided for each solenoidcircuit, and the two circuits are independent of each other.

8!) is a sprocket positioned on a shaft 8i and meshing with the chain13. 82. is a roller or printing cylinder also fixed on the shaft 8! and83 is a gear fixed on that shaft. 84 is a gear fixed on the shaft whichcarries the roller 4'1. This gear meshes with the gear 83 on the shaft8|. 85 is an adjusting means for the spring 54.

Although I have shown an operative form of my invention, it will berecognized that many changes in the form, shape and arrangement of partscan be made without departing from the spirit of the invention, and myshowing is, therefore, to be taken as, in a sense, diagrammatic.

The use and operation of this invention are as follows:

The device as shown is arranged for supplying a continuous web ofmaterial to a printing press or processing machine at constant andadjustable tension. In the preferable form of the device, the speedrelationship of the pulley ill to the elements controlling the passageof the web through the machine to which the web is supplied ispermanently set at a fixed relationship whereby the surface of thepulley i0 is driven by the chain l3 through the sprocket l 2 and shaftII at a speed slightly less than the speed at which the web is drawnfrom the roll by the machine to which it is being supplied. Under theseconditions, the roll being turned by the pull of the web as it is drawnfrom the roll, drives the belts 9 which tend to drive the pulley I0,thereby transmitting power back to the machine to which paper issupplied, which power is supplied to the roll by the pull of machine onthe paper.

In general, under stable operating conditions, the tension in the webwill be closely proportional to the pressure in the cylinders 23. Thispres sure is maintained constant by the reducing and relief valve 61,but may be varied by changing the adjustment of the valve 61. Theuniformity of the tension, being dependent upon a fixed linear speedrelationship, is disturbed by any factor in the operation of the webfeeding machine or in the machine to which the Web is supplied whichdisturbs this linear speed relationship. The primary cause of suchdisturbances is bodily displacement of the roll 8 caused by rotation ofthe shaft 3 and the arms 5 which carry the roll 8. Such movement isnecessary during the operations of loading in a successive roll 8' andin changing from the roll 8 to the roll 8' during the web feedingoperation as the roll 8 nears expiration.

The length of the web 44 between the roll 8 and the roll 46 will bechanged by the bodily movement of the roll.8. Thus movement of the roll"8 away from the pulley 14? requires: the momentary supply 'of additionalpaper from the roll 8 or else" the web- 44 will be'tightenedi up andwill pullwith increased tension. Conversely, movement of the roll: 8toward the pulley 14 will tend to cause a momentary'slackeningzofitheweb. These changes are'compounded'byrthe fact thatmovement' of the arms5"rten'ds toroll'the' roll 8' upon the'b'elt 9 much-like a differentialpulley. Suchdisturbances; while ofsmalliquantitative amount, areseriousin many operations, particularly when the device is :required to=main= tain-constant' tension for register control in -fine colorprinting. because any change in tension will affect the register" of theprinted web, and thereby cause'waste.

Means which will .be: described below are pmvided for varying thepressure in the cylinders upon the appearance of certain conditions"; Inorder-to accomplish the de'sired' control; the-roller 45-"is insertedinthe system'an'd the web M passes over it. Tension-on the-webwillafiect the-position of I the roller 45. Increase-inrthe tension willtend to raise the roller, and decrease in; the tension'will tendtolowerit. A slight variation in the tension will-move the-roller 45 upor=down a distance not great: enough to cause any ac; tion by thecontrols whichare actuated by this movement.

If an up or down movementof the. roller-45 beyond predeterminedlimitsmccurs, the-controls will become effective. Thus,- if tension: onthe web 44 is for somereason reduced;'.the roller: 45 will tend tomove-downwardly. Since theroller is fixed in relation to the shaft 49,its:movement up or down-Will rotate that shaft, carrying the switchoperating arms-5i? and-52 When tension on' the Web 44 isreduced'andthe-roller-45'moves downwardly, the shaft 49- is moved in .aa counter.- clockwise direction as viewed in Figures 1 and 4, and thiscauses the arm-52 to operate theswitch 54-, thus actuating thesolenoid65 and' moving the valve 60 to applypressure on the-brake drum35, and'thus to slow down the-shaft- !5 ,-.the'reby slowing the-movementof the belts-9,- thereby delaying'the discharged the web44 from therollerand increasing the'tension on the web The slowing effect ofbraking force on the brake drum-35-is limited to an amount sufiicient tocause the belt 9 todrag behind the surface speed of the'pulley lllratherthan to tend tolead it. This may be a change of several-percent in thespeedof the belt 9; butthe ability-ofthe pulley I 4 to hold back thebelt 9-is limited-by the fact that excessive braking on thepulleyv I4permits the pulley It to feed excess belt to the pulley [4, therebyloosening: the belt 9 onthe pulley I 4 and permittingit' to slip.-

When the tensionon the web-'44 is increased, the roller 45 is raised,theshaft-49 ismoved in -a clockwise directionand the arm 5-l operatesthe switch 53 to energize the solenoid '15. This moves the valve 69 tobleed pressurefrom theoylinders 2-3, and thus to reducethetensionon-thebelt 9, and hence to permit a freer: discharge" of the web 44.

Each of the operations described may be ofno more than momentaryduration; andv as soon as the condition which caused the'movement' ofthe shaft 49 has been remedied;the roller 45 returns to thenormal'position andbrings the shaft again to that position and-restoresthe switches'to th'eir normal condition. This: operation will repeatitself Whenever unsatisfactory tension conditions develop in the webtMeans-are thus provided to aoperate in' response to:disturbances1 in:-tension to: compensate:fonthezdisturbances automatically;

and hold the tension within very close limits: of control.

It will be seen that the position of the rol'ler' is' determined'byxthe.balance 'b'etween the' pull of the web 44- against: the spring Since;withia given s'etting' of. the springs5fl the'com'e pensating. efiects'and-the: neutral zone will. ale ways occur with the'same tension. in:the: web; and since it is necessary to vary the Web tension to" meetoperating requirements, it is :necessaryto adjust the pressure: appliedto the roller: 45 by-tne' spring 50'. Adjusting means 85, consisting ofa hand wheel and' screw, are-,- therefore, pro vid'ed' at the fl'xed-end of the spring 50 to permit an adjustment'of thepressure' exerted bythe spring.

In the present disclosure the members-41 and 82 represent apressure'nip, or a printing couple, included in such a machine, and theymaybe disposed to draw the web from its-sourceointh'e roll 8' at arateof'speed' fixed in relationshipto their speed of rotation. As hereshown, a-= gear 84 on the extended shaft of the roller orcylinder 41meshes with a gear 8-3 on the-extended shaft BI'Of-th'e roller orcylinder 82; which alsocarries the-sprocketfifl meshingwith the chain l3which engages the teeth of the sprocket l2 on the shaft 'H.-

Thus, it will beseen that ther is a fixed speed relationship between thesurface of the rollers 4'5 and 82 and-"th'eWebM whichpasses and isnipped betweenthem, and the surface of the pulleys Hi5 Inthepreferredformof the device, the gear" ratios and diameters of' theelements are 50 selected that the'surfaceof' the pulleys I 9 moves atslightly lower speed than the surfaceofthe rollers l'i andB-Z'and'theweb 44';

It s'hould'be noted that the rollers 41- and 82 are a partof amachine'outside the-ma'chine-of this invention, whichmachine isseparately driven; Th actual form ofthis-outside'device is immat'erialto thepresent invention; and, in fact, maytake the formof a drivensuction'apron; S rolls, or anytype of device capa'ble'of exert-'- in'gpull* on the Web: In all cases, however, the pulleys it should have'afixed speed relationship to-thesaidpulling device-iorthe best results:

1- In combination in a web' unwinding-mecha nism,- means f'orsupportinga roll of web to be unwound; and means for-rotating said web; saidrotatingmeansincluding a belt, a member in cont'actwithsaid belt, abrake adaptedto affect said rnember, a tension varying device in contactwith saidb'elt, means'for operatin said dev-ice to vary the tension or"said belti andtension'com trol-means, said'control means comprisinga'roller mountedforcontact witlisaid web after it leaves the" roll, andsupporting means for said roller, spring means effective on said rollerto move'it agalns-t' saidwveb, an'd'a pair of switches; a' pair ofswitch operatih members positioned to opcrate said switches; said switchoperating mendbers positioned to be'moved by the movement of said"roller, one of said switches connected to said brake; theoth'er' ofsaid'switches connected to said tension varyingdevice, whereby move"-m'e'nt of the roller in one'direction-is effective-to operate saidbrake, and' movement of saidroller in the opposite direction iseffective-tovary'the tension varying device.

2;- ln combination in a web unwindingme'chanism, means for automaticallyand intermittently adjusting the tension of said web asit is 1211-wound, said means including a movable member in contact with said weband parts operated in response to the movement of said member to varythe tension of said web, said mechanism including means for holding aroll of web, and a belt for rotating said web, and a pressure operatedtake-up device in contact with said belt for Varying its movement tocontrol the tension of the web, the said parts being connected to saidpressure operated take-up device and actuating them in response tomovement of said member to re duce the pressure in said pressureoperated takeup device, said varying devices including a pressurecylinder and a valve for bleeding pressure from it, and means foractuating said bleeding valve in response to the movement of said firstmentioned tension adjusting means.

3. In combination in a web unwinding mechanism, means for controllingthe tension of the web as it is unwound, said means including anapparatus for supporting a roll of web, and a rotating means for saidroll, said rotating means including a belt, a brake member in contactwith said belt, and a fluid pressure tensioning device in contact withsaid belt, a valve for bleeding pressure from said tensioning device anda movably mounted roller in contact with said Web after it leaves theroll, and parts adapted to be moved by said roller, one of them effectivupon said brake and another upon said fluid pressure tensioning deviceto reduce the pressure in said device, and means for actuating saidbleeding valve in response to the movement of said first I mentionedtension adjusting means.

4. In combination in a web unwinding mechanism, means for supporting aroll of web to be unwound, and means for rotating said web, saidrotating means including a belt, a member in contact with said belt, abrake adapted to affect said member, a tension varying device in contactwith said belt, means for operating said device to vary the tension ofsaid belt, and tension control means, said control means comprising aroller mounted for contact with said web after it leaves the roll, andsupporting means for said roller comprising a pair of arms, spring meansefiective on said roller to move it against said web, and a pair ofswitches, a pair of switch operating members positioned to operate saidswitches, said switch operating members positioned to be moved by themovement of said roller, one of said switches connected to said brake,the other of said switches connected to said tension varying device,whereby movement of the roller in one direction is effective to operatesaid brake, and movement of said roller in the opposite direction iseffective to vary the tension varying device.

5. In combination in a web unwinding mechanism, means for supporting aroll of web to be unwound, and means for rotating said web, saidrotating means including a belt, a member in contact with said belt, abrake adapted to affect said member, a tension varying device in contactwith said belt, means for operating said device to vary the tension ofsaid belt, and tension control means, said control means comprisin aroller mounted for extended contact with said web after it leaves theroll, and supporting means for said roller comprising a pair of arms,spring means effective on said roller to move it against said web, and apair of switches, a pair of switch operating members positioned tooperate said switches, said switch operating members positioned to bemoved by the movement of said roller, one of said switches connected tosaid brake, the other of said switches connected'to said tension varyingdevice, whereby movement of the roller in one direction is effectiv tooperate said brake, and movement of said roller in the oppositedirection is efiective to vary the tension varying device.

6. In combination in a web unwinding mechanism, means for supporting aroll of web to be unwound, and means for rotating said web, saidrotating means including a belt, a member in contact with said belt, abrake adapted to afiect said member, a tension varying device in contactwith said belt, means for operating said device to vary the tension ofsaid belt, and tension control means, said control means comprising aroller mounted for contact with said web' after it leaves the roll, andsupporting means for said roller comprising a pair of pivoted arms,spring means effective on said roller to move it against said web, and apair of switches, a pair of switch operating members positioned tooperate said switches, said switch operating members positioned to bemoved by the movement of said roller, one of said switches connected tosaid brake, the other of said switches connected to said tension varyingdevice, whereby movement of the roller in one direction is effective tooperate said brake, and movement of said roller in the oppositedirection is effective to vary the tension varying device.

7. In combination in a web unwinding mechanism, means for supporting aroll of web to be unwound, and means for rotating said web, saidrotating means including a belt, a member in contact with said belt, abrake adapted to affect said member, a tension varying device in contactwith said belt, means for operating said device to vary the tension ofsaid belt, and tension control means, said control means comprising aroller mounted for contact with said web after it leaves the roll, andsupporting'means for said roller comprising a pair of pivoted, counterweighted arms, spring means effective on said roller to move it againstsaid web, and a pair of switches, a pair of switch operating memberspositioned to operate said switches, said switch operating memberspositioned to be moved by the movement of said roller, one of saidswitches connected to said brake, the other of said switches connectedto said tension varying device, whereby movement of the roller in onedirection is effective to operate said brake, and movement of saidroller in the opposite direction is effective to vary the tensionvarying device.

8. In combination in a web unwinding mechanism, means for supporting aroll of web to be unwound, and means for rotating said web, saidrotating means including a belt, a member in contact with said belt, abrake adapted to affect said member, a tension varying device in contactwith said belt, fluid pressure means for operating said device to varythe tension of said belt, and tension control means, said control meanscomprising a roller mounted for contact with said web after it leavesthe roll, and supporting means for said roller comprising a pair ofarms, spring means efiective on said roller to move it against said web,and a pair of switches, a pair of switch operating members positioned tooperate said switches, said switch operating members positioned to bemoved by the movement of said roller, one of said switches connected tosaid brake, the other of said switches connected to said tension varyingdevice, whereby movement of the roller in one direction is effective tooperate said brake, and movement of said roller in the oppositedirection is eiiective to vary the pressure in said fluid pressure ofsaid tension varying device.

9. In combination in a web'unwinding mechanism, means for supporting aroll of web to be unwound, and means for rotating said web, saidrotating means including a belt, a member in contact with said belt, abrake adapted to affect said member, a tension varying device in contactwith said belt, fluid pressure means for operating said device to varythe tension of said belt, and tension control means, said control meanscomprising a roller mounted for extended contact with said web after itleaves the roll, and supporting means for said roller comprising a pairof pivoted arms, spring means effective on said roller to move itagainst said web, and a pair of switches, a pair of switch operatingmembers positioned to operate said switches, said switch operatingmembers positioned to be moved by the movement of said roller, one ofsaid switches connected to said brake, the other of said switchesconnected to said tension varying device, whereby movement of the rollerin one direction is efiective to operate said brake, and movement ofsaid roller in the opposite direction is effective to vary the pressurein said fluid pressure of said tension varying device.

10. In combination in a web unwinding mechanism, means for supporting aroll of web to be unwound, and means for rotating said web, saidrotating means including a belt, a member in contact with said belt, abrake adapted to afiect said member, a tension varying device in contactwith said belt, fluid pressure means for operating said device to varythe tension of said belt, and tension control means, said control meanscomprising a roller mounted for extended contact with said web after itleaves the roll, and supporting means for said roller comprising a pairof pivoted, counterweighted arms, spring means efiective on said rollerto move it against said web, and a pair of switches, a pair of switchoperating members positioned to operate said switches, said switchoperating members positioned to be moved by the movement of said roller,one of said switches connected to said brake, the other of said switchesconnected to said tension varying device, whereby movement of the rollerin one direction is efiective to operate said brake, and movement ofsaid roller in the opposite direction is effective to vary the pressurein said fluid pressure of said tension varying device.

11. In combination in a web roll unwinding and web tensioning system,means for supporting a roll of web rotatively, means for drawing out theweb from said roll, means defining a belt in contact with said roll forcontrollably restraining the rotation of said roll, rotative meansdefining a pulley in contact with said belt and having a fixed speedrelationship to said web drawing means, pressure means for controllingthe tension in said belt, tension determining means comprising a movablemember in contact with said web between said roll and said web drawingmeans, means for positioning said tension determining means against thepull of said web, means for momentarily reducing the speed of said belt,means for reducing the restraining effect of said belt, and means foractuating either of said last two means according to the position ofsaid ten-- sion determining means.

12. In combination in a web roll unwinding and web tensioning system,means for supporting roll of web rotatively, means for drawing out s droll for controllably restraining the rotation of L roll, rotative meansdefining a pulley in contact with said belt and having a fixed speedrelationship to said web drawing means, pressure means for controllingthe tension in said belt, tension determining means comprisa movablemember in contact with said web between said roll and said web drawingmeans, means for positioning said tension determining means against thepull of said web, means for momentarily reducing the speed of said beltcomprising a brake and a puliey in contact with said belt, means forreducing the restraining efiect of said belt comprising means forreducing pressure in the pressure means, and means for actuating eitherof said last two means according to the position of said tensiondetermining means.

13. In combination in a web roll unwinding and web tensioning system,means for supporting a roll of web rotatively, means for drawing out theweb from said roll, means defining a belt in contact with said roll forcontrollably restraining the rotation of said roll, rotative meansdefining a pulley in contact with said belt and having a fixed speedrelationship to said web drawing means, pressure means for controllingthe tension in said belt, tension determining means comprising a movablemember in contact with said web between said roll and said web drawingmeans, means for positioning said tension determining means against thepull of said web, means for momentarily reducing the speed of said beltcomprising a brake and a pulley in contact with said belt, means forreducing the restraining effect of said belt comprising means forreducing pressure in the pressure means, and means for actuating eitherof said last two means according to the position of said tensiondetermining means comprising a switch and control means and a rotarymember in contact with said web, mounted to actuate said switch and saidcontrol means.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 731,530 Wood June 23, 1903 1,618,975 Cline et al. Mar. 1, 19271,972,916 Broms Sept. 11, 1934 2,064,638 Wheldon et al. Dec. 15, 19362,334,164 Lotz Nov. 16, 1943

